This invention relates to electrometers and has for its principal object, the first, reduction of the effects of environmental changes on high impedance electrometers operating in hostile environments such as temperature changes, vibration, contamination, and humidity and, secondly, to increase substantially the speed of response of electrometer.
In the art of mass spectrometry where this invention is useful, it is necessary to accurately detect or measure very small currents, ion currents, in the order of 1 femto ampere, to determine the constituency of a gas. Additionally, it may be necessary to measure these changes rapidly.
To do this, a detector must operate with high speed and be highly sensitive to detect such small current values. Today's measuring devices have been unable to meet this criteria. For example, today's detectors respond to an input current change in 30 to 100 milliseconds (10% to 90% time) whereas with this invention not only is it able to measure low values of current (1 femto amp) but is able to do so in less than 1 millisecond response time. With this invention the capabilities of a mass spectrometer are no longer inhibited since the response time of the electrometer is now typically 100 times faster than the prior art electrometer.
Thus, an object of this invention is to provide a very sensitive high impedance electrometer capable of operating with a mass spectrometer so as to measure extremely low current values and which has a fast response time as to improve the operation of mass spectrometers.
Another object of this invention is to provide a high impedance electrometer having improved performance (speed and sensitivity) due to the minimization of the effects of internal shunt capacitances in and around the high impedance components.
Other and additional objects of this invention will become apparent to those skilled in the art from a study of the drawings and the description thereof and from the more detailed description of the invention hereinafter, as for example, the use of this invention with any device having very small output currents which need an electrometer of this type to measure these currents quickly.